1. Field of the Invention
The present invention relates to a lens barrel having an image-shake correcting optical system arranged to correct image shakes caused by vibrations imparted to an optical apparatus and an optical system arranged to move along an optical axis during focusing or zooming.
2. Description of Related Art
The cameras of nowadays are arranged, by the art of automatic exposure and the art of automatic focusing, to automatically decide an exposure and automatically drive a focusing optical system. Therefore, the probability of failure in taking pictures has become very small even for persons unfamiliar with camera operations.
Further, studies and researches for correction of image shakes due to vibrations imparted to cameras have advanced. Therefore, factors of a photo-taking failure have almost completely been removed for camera users.
In brief, the system for correcting image shakes due to camera vibrations is described as follows. The camera vibration taking place in taking a shot is about 1 to 12 Hz in frequency. To permit photo-taking without any image shake even in the event of camera vibration, the image-shake correcting system is basically arranged to detect the camera vibration and to displace a correction lens according to the value of vibration thus detected.
Therefore, for this purpose, it is necessary, first of all, to accurately detect the camera vibration and then to correct an optical axis deviation caused by the camera vibration by displacing a correction lens according to the result of detection.
Theoretically, the vibrations of a camera can be detected by providing the camera with a vibration detecting means for detecting acceleration, angular velocity, etc., and a displacement information output means for outputting displacement information by electrically or mechanically integrating an output signal of the vibration detecting means. Image shakes can be corrected by controlling, according to the displacement information, a correcting optical unit disposed within an image-shake correcting device which is arranged to vary a photo-taking optical axis by displacing a correcting optical system.
Conventional known driving means for driving the correcting optical system include a driving device, in which a coil and a magnet are used, the coil or the magnet is disposed at a fixed part, the magnet or the coil is disposed at the correcting optical system, and a driving part is arranged to drive the correcting optical system by applying a current to the coil. This driving device is arranged in two units and in a pair. The two units are arranged respectively to detect vibrations vertically and horizontally taking place (hereinafter referred to as xe2x80x9cpitchxe2x80x9d and xe2x80x9cyawxe2x80x9d directions), with the camera set in its normal posture, and to drive the correcting optical system independently of each other in the two directions according to the respective vibrations detected.
However, when the camera is arranged to drive the image-shake correcting optical system in addition to driving a focusing optical system or a magnification varying optical system, the increase in number of optical systems to be driven results in an increase in number of such optical systems that are tilted by a change in the photo-taking posture of the camera. If a tilt takes place in an optical system under such a condition, the optical performance of the camera tends to deteriorate because, for example, an image would be formed on the front side or on the rear side of a film surface at an upper, lower, right or left part of the film surface, although the image can be adequately formed on the film surface at the center thereof.
Such a tilt must be suppressed by minimizing the clearance or play of each driving part, therefore. However, the efforts to minimize the play of each driving part cause an increase in driving load to greatly deteriorate the characteristic of driving, particularly, with regard to the driving of the focusing optical system or the image-shake correcting optical system, which is automatically driven.
The invention is directed to the solution of the problem of the prior art described above. It is, therefore, an object of the invention to provide a lens barrel arranged to be capable of preventing the optical performance thereof from being deteriorated by tilting of optical systems without deteriorating the driving characteristics for driving a focusing optical system, a magnification varying optical system and an image-shake correcting optical system.
To attain the above object, according to the invention, positions of support parts or protruding parts for respectively restraining tilts of optical axes of a focusing optical system and an image-shake correcting optical system, which are shifted forward or rearward in an optical axis direction with respect to respective positions of centers of gravity of the focusing optical system and the image-shake correcting optical system, are set in correspondence with the relationship between tilts of the focusing optical system and the image-shake correcting optical system and directions of tilts of an image plane resulting from the tilts of the focusing optical system and the image-shake correcting optical system.
More specifically, according to one aspect of the invention, there is provided a lens barrel comprising a first holding tube holding a first optical system arranged to be driven in a direction perpendicular to an optical axis for correcting an image shake, a second holding tube holding a second optical system arranged to be moved along the optical axis, a first plurality of projections arranged at the first holding tube to protrude perpendicularly to the optical axis for restraining the first optical system from tilting with respect to the optical axis, and a second plurality of projections arranged at the second holding tube to protrude perpendicularly to the optical axis for restraining the second optical system from tilting with respect to the optical axis, wherein positions of the first plurality of projections and the second plurality of projections are respectively shifted with respect to positions of centers of gravity of the first holding tube and the second holding tube in the optical axis direction.
In particular, in the lens barrel, the positions of the first plurality of projections and the second plurality of projections are shifted in phase.
Further, in the lens barrel, if a direction of tilting of an image plane caused by tilting of the first optical system and a direction of tilting of the image plane caused by tilting of the second optical system are the same, a direction in which the position of the first plurality of projections is shifted with respect to the position of the center of gravity of the first holding tube and a direction in which the position of the second plurality of projections is shifted with respect to the position of the center of gravity of the second holding tube are opposite to each other.
Further, in the lens barrel, otherwise, if a direction of tilting of an image plane caused by tilting of the first optical system and a direction of tilting of the image plane caused by tilting of the second optical system are opposite to each other, a direction in which the position of the first plurality of projections is shifted with respect to the position of the center of gravity of the first holding tube and a direction in which the position of the second plurality of projections is shifted with respect to the position of the center of gravity of the second holding tube are the same.
Further, in the lens barrel, the second optical system is arranged to move along the optical axis for focusing.
Further, in the lens barrel, the second optical system is arranged to move along the optical axis for zooming.
The above and further objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.